The present invention relates to transferring apparatuses and robot arms, and more particularly to transferring apparatuses and robot arms for transferring semiconductor wafers and liquid crystal substrates.
Generally, semiconductor devices are produced from semiconductor wafers by sequentially sending each wafer into a plurality of chambers that are maintained in high temperature and high vacuum states. The semiconductor wafers are first stocked at a loading station and then sent to a preparing chamber. From the preparing chamber, the wafers are sent to each processing chamber. A transferring apparatus provided with a robot arm is used to transfer the wafers between the loading station and the preparing chamber, between the preparing chamber and the processing chambers, and between the processing chambers. Such transferring apparatus must have superior heat resistance characteristics and must be capable of preventing dust from arising.
Belt drive type robot arms and linkage type robot arms are known in the prior art. A typical belt drive type robot arm is provided with a hand to carry wafers and a motor to move the hand along a certain plane. Such a robot arm employs a belt drive mechanism that includes a plurality of belts and arms to transmit the drive force of the motor to the hand.
The drive mechanism includes a first arm, the proximal end of which is connected to the motor's output shaft, or first rotary shaft. The proximal end of a second arm is rotatably connected to the distal end of the first arm by means of a second rotary shaft. The hand is connected to the distal end of the second arm by means of a third rotary shaft.
The drive force of the motor is transmitted to the hand by way of a drive pulley, which is coupled to the first rotary shaft, two intermediate pulleys, which are coupled to the second rotary shaft, a driven pulley, which is coupled to the third rotary shaft, and two belts, which connect the pulleys. The rotation of the motor output shaft causes the hand to move along a certain plane. The movement of the hand allows the wafers to be transferred.
This type of robot arm is provided with a magnetic fluid seal that is attached to the vicinity of the proximal end of the hand. The seal prevents dust, which arises from the bearing of each pulley during rotation of the pulley, from entering the chambers. However, the seal has a tendency to deteriorate due to exposure to the heat of the chambers. Progressive deterioration increases the amount of dust that arises. This is inefficient since it is necessary to frequently exchange the seal.
The arms of the robot arm extend and contract to transfer the wafers. During contraction, the arms overlap one another. Accordingly, the opening of each chamber must be large enough to accommodate the overlapping arms and the wafers. Large openings are disadvantageous since the environment in each chamber must be maintained in a high temperature and high vacuum state.
Japanese National Phase Patent Publication No. 7-507010 (WO 94/14581) describes a joint arm, which is a typical linkage type robot arm. The joint arm includes a shoulder portion, an elbow portion, and a wrist portion. A pair of upper arms (corresponding to the first arms of the above robot arm) are arranged rotatably about the shoulder portion. A pair of lower arms (corresponding to the second arms of the above robot arm) are arranged rotatably about the wrist portion.
An intermediate link having a plurality of shafts connects the upper arms to the lower arms at the elbow portion.
The intermediate link has two S-shaped strips. The strips transmit the pivoting of the elbow portion of the upper arm to the corresponding elbow portion of the lower arm. An end effector (corresponding to the hand of the above robot arm) is attached to the wrist portion of the pair of upper arms. Among the two upper arms, only one is driven.
When one of the upper arms is pivoted about the elbow portion, the pivoting is transmitted to the end effector. This moves the end effector. Accordingly, semiconductor wafers are transferred by placing the wafers on the end effector.
However, the pair of upper arms and pair of lower arms in the prior art linkage type robot arm are formed from rigid and prism-like solid bodies. Furthermore, the upper arm and the lower arm are connected to each other by the intermediate link, which includes a plurality of shafts, and the S-shaped strips. This increases the weight of the arms and necessitates a strong driving force. The dimensional accuracy and rigidity of the shafts must also be enhanced to move the heavy arms smoothly. Furthermore, the S-shaped strips have a special shape and are not easily available. As a result, the manufacturing and assembling of the robot arm is burdensome. This increases the production cost of the robot arm.